Myth vs. Fact -- "the fineness of detail from each pixel..."

From Rob Galbraith: "The EOS-1D Mark III produces the best overall file of any digital SLR we've ever used. A CR2 coming from this camera contains a level of detail, dynamic range, tonality and overall quality that is hard to match. The Nikon D3, for example, produces a better NEF at really high ISO settings (plus very good quality generally), but at lower ISOs it can't quite deliver the fineness of detail from each pixel that the EOS-1D Mark III does."

From Ken Rockwell: "...either Canon [5D or 1Ds Mk III] has finer detail than the Nikon, and the 1Ds has finer detail then the 5D. It makes sense that the Nikon has less fine detail: the D3 is a sports, news and action camera optimized for speed, while each of these Canons is much slower and optimized for fine image quality."

So, the question is, "Is there really a seeable, measurable difference in the "fineness of detail from each pixel" which places Nikon's best files at an IQ disadvantage over Canon's best for all but the highest ISO shots?